This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Cardiac fibrillation is disorganized electrical behavior of the heart, and its consequence is the loss of coordinated muscle contraction. Electrical defibrillation by timely application of a strong electric shock to the heart has long been used as an effective therapy for this otherwise lethal disturbance of cardiac rhythm. In recent years defibrillation therapy has dramatically expanded due to its improved accessibility and functionality. Despite the critical role that the technique plays in saving human life, the fundamental mechanisms by which electrical shocks halt life-threatening disturbances in cardiac rhythm are not completely understood. Mechanical contraction follows the electrical activation of the heart. However, it has long been known that there is a cross-talk between the electrical and mechanical processes which could play a role in anti-arrhythmia therapy. Owing to the complexities in cardiac structure and behavior, mechanical contributions have never before been considered in the investigation of cardiac defibrillation mechanisms. The objective of this research is to determine the contribution of mechanoelectrical feedback in the process of cardiac defibrillation, and thus, to increase our knowledge of the mechanisms by which the exposure of the heart to strong electric shocks terminates fibrillation. This application seeks to establish collaboration between the Computational Cardiac Electrophysiology Group at Tulane University and the National Biomedical Computation Resource and thus, to take full advantage of the combination of state-of-the-art approaches in modeling cardiac defibrillation and mechanical contraction, respectively, developed by the two groups. Upon completion, the project is expected to bring a new level of understanding to how the complex electro-mechanical events in the heart can be used to benefit anti-arrhythmia therapy. As a collaborative project of the NBCR this research will promote extensions to the development of Continuity and its anatomic, electrical and mechanical models and algorithms that will permit greater integration with bidomain models of the heart and torso, opening in up to the large array of applications in cardiac pacing, shock and electrocardiography.